HAIFA, ISRAEL — With the Syrian civil war threatening almost daily to spill over the border into Israel, there is a quiet tension in the air at Rambam Health Care Campus.

Northern Israel’s largest hospital was at the heart of a month-long Hezbollah rocket barrage during the bloody 2006 conflict with the Lebanese militia and would undoubtedly be in the thick of action again if the Syrian regime or its Hezbollah allies turned their weapons south.

“Today it’s very peaceful, but tomorrow or the next day, someone could start shooting,” said Shimon Reisner, a cardiologist and Rambam’s deputy director. “You never know. We are used to that, we live with that.”

Unlike 2006, however, the Mediterranean-seaside hospital believes it will be more than ready if it comes under attack once more.

The close calls seven years ago have given rise to an extraordinary construction project: the world’s largest, fortified underground hospital, three below-grade storeys — 20,000 square metres — that can be rapidly converted into a full-service general hospital with room for 2,000 beds.

The vast space will be used as a parking lot in peacetime, but oxygen and other gas lines, suction tubes and electricity have been installed in the walls to enable a quick makeover. Next to each parking space, locked, plastic covers hide sockets for those services until they are needed. There are even outlets for toilets and other plumbing hidden throughout the walls, and cutting-edge protection against chemical or biological warfare.

The subterranean health centre suddenly seems particularly prescient, given threats from Syria and Hezbollah to attack Israel air strikes against Syrian targets believed to have been carried out by the Israelis. Though most of the country’s enemies now have longer-range weapons that could hit anywhere in Israel, cities close to the northern borders are still considered at heightened risk. Lebanon is just 25 kilometres from Haifa, Syria about 70 km.

The project also underscores the bunker culture Israelis take almost for granted, part of living in a country that has been at war routinely over its 65-year history.

Israeli homes are required by law to have access to a bomb shelter and rooms that can be sealed off in case of a chemical attack. More than 100 bus shelters in Sderot, near the Gaza Strip, have been specially reinforced to provide refuge to pedestrians during an attack. The government has distributed millions of gas masks.

A Tel Aviv hospital already has a much smaller underground facility and another is being built at a hospital near Gaza.

Sharon Architects

“Everything within seven kilometres of the Gaza Strip is protected [from rocket attacks]: schools can keep on going during an air raid,” said Capt. Eytan Buchman, a spokesman for the Israel Defence Forces.

The 2006 conflict with Hezbollah brought home for Rambam the potential threats even from a relatively lightly armed adversary.

Prof. Reisner recalls clearly the explosions that marked the beginning of the hospital’s ordeal.

“I spent many years in the army and I know how Katyusha rockets sound,” he said.

“We were sitting here and it was Sunday morning, 9 o’clock and I started counting: ‘One, two, three, four’ Katyusha missiles. They have a very specific sound — a whistle and boom … I said, ‘The war has started.’ ”

Israel has been criticized for responding disproportionately when Hezbollah appeared to have kidnapped two Israeli soldiers near the border, killed three others and fired several rockets at nearby towns. About 1,000 Lebanese, including hundreds of civilians, died in the subsequent Israeli ground invasion and bombing campaign.

Yet the rockets fired from Lebanon killed 44 Israeli civilians — among 165 total deaths — and injured about 1,500 more, typical of recent conflicts in the region that have taken a major toll on Israeli non-combatants.

Rambam also happens to be next door to a major military target: Israel’s main naval base. By the time the war ended in mid-August 2006, about 60 rockets had crashed into Haifa within a couple of kilometres of the hospital, a major trauma centre where many of the war wounded were treated. Some landed metres from Rambam’s grounds.

“We were standing there, listening to rockets falling all around us, walls were shaking and our own staff were being brought in with injuries,” Dr. Michael Halberthal, a Rambam emergency physician, said in a hospital newsletter.

The institution eventually set up a makeshift sick bay in its basement, but it had room for only a fraction of the patients.

With literally a handful of exceptions, all the healthy staff showed up for work, regardless of race or creed, said Prof. Reisner. His workforce is unusual in Israel: 25% of the doctors and many department heads are Arab, while a Muslim prayer room sits next to the hospital synagogue, said David Ratner, a hospital spokesman.

We were standing there, listening to rockets falling all around us, walls were shaking and our own staff were being brought in with injuries

It is a hospital accustomed to being at the centre of the Arab-Israeli conflict: after the controversial Israeli commando raid on a Turkish boat trying to break the Gaza blockade in 2010, injured Israeli soldiers and Turkish activists lay side by side in Rambam’s trauma bay.

As the dust settled from the 2006 Hezbollah clash, Rambam reinforced its emergency department to withstand a heavy barrage, installing blast doors to seal it off from the rest of the building during attacks.

The hospital also decided to redirect funds from other expansion projects to an underground mirror of its above-surface services.

As well as threading patient-care utilities through the walls of the cavernous underground space, an Israeli company installed a state-of-the-art ventilation system that can keep the subterranean wards safe from the effects of chemical and biological weapons, said Mr. Ratner.

Retractable soft-sided ducts, hidden away while peace reigns, can be pulled out to provide air conditioning to patients in wartime.

But we are always ready … If we look at the Middle East, it’s quite possible we will use it one day

Converted to hospital mode, the underground facility will have an intensive-care unit, four operating rooms, space for 94 kidney-dialysis patients and delivery rooms.

But what if the $350-million project is never needed, making it perhaps the best-equipped, most-expensive parking lot in the world? At Rambam, no one seems to worry about that potential; Mr. Ratner is even afraid its scheduled completion date in a few months will not be soon enough.

“Officially there is no alarm,” said Prof. Reisner.

“But we are always ready … If we look at the Middle East, it’s quite possible we will use it one day.”